Preparation of 5-cyanotetrazoles



United States Patent Ofifice 3,021,337 PREPARATIDN F S-CYANOTETRAZOLESLucille Theresa Morin and Ken Matsuda, both of Stamford, Conn.,assignors to American Cyanamid Company, New York, N.Y., a corporation ofMaine No Drawing. Filed May 6, 1960, Ser. No. 27,284 4 Claims. (Cl.260-308) The present invention relates to the novel preparation ofS-cyanotetrazole. More particularly, it relates to the synthesis of5-cyanotetrazole utilizing l-cyanoformimidic acid hydrazide by thesimultaneous nitrosation and ring closing of the same.

It is known that S-cyanotetrazole can be prepared by' reacting hydrazoicacid with cyanogen. The use of such reagents, especially in large scaleoperations, creates a serious safety hazard problem. There has been aneed to provide a process capable of yielding premium grade5-c-yanotetrazole in good yield while lessening the dangers inherent inthe prior art reaction.

It is, therefore, a principal object of this invention to provide anovel process for the preparation of 5-cyanotetrazole. It is a furtherobject to provide a process for the preparation of S-cyanotetrazolewhich is capable of being carried out in the presence of a relativelystable and safe reactant. It is still a further object to provide aprocess for the preparation of S-cyanotetrazole from 1- cyanoformimidicacid hydrazide. Other objects and advantages of the invention will beapparent to those skilled in the art from the consideration of theensuing disclosure.

To these ends, l-cyanoformimidic acid hydrazide can be reacted in astraightforward manner by the simultaneous nitrosation and ring closureof the hydrazide reactant. This is surprisingly accomplished by theutilization of alkali nitrite in the presence of nitric acid.

In accordance with the process of this invention, it has been found thatl-cyanoformimidic acid hydrazide is readily ring closed by means of analkali metal nitrite in the presence of nitric acid and then recoveringthe thus-formed l-cyanotetrazole. Advantageously, the ring closure canbe eflected over a relatively Wide range of temperatures generallybetween 25 C. and +25 C., and preferably at between C. and +10 C. It hasbeen further found that the amounts of reactants are not critical. Theaddition of suflicient alkali metal nitrite is the sole prerequisiteand, generally, equimolar amounts of the hydrazide reactant and thenitrite are sufficient to effect the desired ring closure and to obtaina premium product in good yields.

It will be noted that the preparation of S-cyanotetrazole principallyinvolves a sequence of four stages:

First, l-cyanoformimidic acid hydrazide is dissolved in aqueous nitricacid. Although the amount of nitric acid employed is not critical,sufiicient acid should be present to maintain the reactants in solution.

Second, the process involves the addition of a soluble silver salt, suchas silver nitrate, to the aforementioned solution of stage 1. Hereagain, it is preferred to utilize equimolar amounts of silver nitrateand 1-cyanoformimidic acid hydrazide. The addition of the silver nitrateis generally carried out at a temperature between about -25 C. and +25C. At this stage additional nitric acid may be required to maintain thereactants in solution.

Third, an aqueous solution of an alkali metal nitrite is then added tothe aforementioned reaction mixture. Insofar as the amount of nitrite isconcerned, this too is not critical, except that the minimum amountshould be equimolar to the l-cyanoformimidic acid hydrazide. It is,however, a good practice to slowly add alkali metal nitrite to thereaction in equimolar amounts with re Patented Feb. 13, 1962 spec-t tothe hydrazide. Illustrative alkali metal nitrites are sodium nitrite,potassium nitrite and lithium nitrite. At this stage, precipitation isnoted. Formation of the silver salt of 5 -cyanotetrazole occurs.

Fourth, precipitated silver salt of S-cyanotetrazole is removed from thereaction medium by conventional means and then washed with water toremove all residual nitric acid. The aqueous menstruum is separated.Additional water is added to the residue. Hydrogen sulfide or anequivalent thereof is bubbled into the aqueous medium. Insoluble silversulfide is precipitated. Simultaneously, S-cyanotetrazole is solubilizedin the aqueous medium. The latter is separated, for example, byfiltration to remove insoluble silver sulfide. The aqueous medium isnext evaporated to recover S-cyanotetrazole.

Thus, the sequence of steps outlined above represents the preferredembodiment of the practice of the invention. However, variations inthissequence are Within the purview and contemplation of the invention.Thus, for example, stage 3 which involves the addition of an alkalimetal nitrite may be reversed with respect to stage 2 directed to theaddition of silver nitrate. Stated otherwise, the addition of an alkalimetal nitrite may precede the addition of silver nitrate. Preceding inthis alternative manner, ring closure of soluble S-cyanotetrazole iseffected. It has been found, however, that the reaction is less easilycontrolled and for this reason is not the preferred embodiment of theinvention.

The reactant, l-cyanoformimidic acid hydrazide, is a novel compound andits method of preparation is set forth with particularity in a copendingapplication for Letters Patent, Serial No. 796,202, filed March 6, 1959.In general, the reactant can be prepared by reacting equimolar amountsof cyanogen and hydrazine.

In order to facilitate an understanding of the process of the invention,the following examples are presented. It is, however, understood thatthese are merely illustrative and are not to be taken as limitative ofthe invention. All parts and percentages are by weight unless otherwisenoted.

EXAMPLE A Preparation of intermediate reactant-1 -cyan0- formimidic acidhydrazide To a stirred solution of 156 parts of cyanogen in 1000 partsof dioxane at 3 C. to 10 C., there is added over a period of 2.5 hours asolution of 96 parts of hydrazine in 330 parts of a dioxaue-methanol(10-1) mixture. Crystallization begins after about one-half hour and thesolution gradually turns orange. After the addition of hydrazine iscompleted, agitation is continued for an additional one-half hour atabout 5 C. The product is collected by filtration as 208.3 parts oflight orange solid melting at 73 C.77 C. It is recrystallized fromethylene dichloride yielding yellow plates, melting at 83 C.- 86 C.Analysis of the l-cyanoformimidic hydrazide thus prepared is as follows:

Calculated: C, 28.57; H, 4.8; N, 66.64; mol wt. 84.08. Found: C, 29.26;H, 4.94; N, 65.73; mol wt. 86.5.

This intermediate is next cyclized in accordance with the followingprocedure.

Example 1 2.0 parts of l-cyanoformimidic acid hydrazide (0.024 mol) asprepared in Example A above are dissolved in 50 parts of water. 20 partsof dilute nitric acid are added to the solution cooled to 5 C. 4.0 parts(0.024 mol) of silver nitrate are then added to the solution which iscooled to about 0 C. An additional 15 parts of concentrated nitric acidare added to the reaction mixture in order to maintain the lattermixture in solution. To the solution 1.7 parts (0.024 mol) of sodiumnitrite (dis- 3 solved in 20 parts of Water) are then added dropwisewith stirring. Cyclization to the tetrazole derivative is rapidlyeflected, since precipitation is immediately noted. When precipitationterminates on inspection, the reaction mixture is ,filteredand theprecipitant washed with copious amounts of water to remove nitric acidwhich dissolves therein. Upon filtration, the residual solid silver saltof 5-cyanotetrazole is then added to 100 parts of water. Hydrogensulfide gas is next passed into the solution to convert the silversaltto soluble S-cyanotetrazole. Removal of insoluble silver sulfide isefifected by filtration. The aqueous filtrate is evaporated to recoverone part of S-cyanotetrazole, a light orange solid. When crystallizedfrom benzene, white crystals are obtained which reddened at 95 C. anddecomposed at about 103 C., analyzing as follows:

Calculated: C, 25.27; H, 1.06; N, 73.66; mol wt. 95.05. Found: C, 25.00;H, 1.27; N, 73.96; mol wt. 94.3.

The product produced by the process of the invention is useful as aninsecticide.

Example 2 the latter solution is added Nasturtium aphids are the lattersolution and a 100% kill is We claim:

1. A process for the preparation of S-cyanotetrazole which comprises thesteps of: reacting 'l-cyanoformimidic acid hydrazide with an alkalimetal nitrite in the presence of nitric acid and a soluble silver saltto effect nitrosation and cyclization of said hydrazide; and thereafterrecovering S-cyanotetrazole thus-formed.

2. A process for the preparation of S-cyanotetrazole which comprises thesteps of: reacting l-cyanoformimidic acid hydrazide in an aqueoussolution containing a mixture of nitric acid and silver nitrate, withaqueous alkali metal nitrite whereby the silver salt of S-cyanotetrazoleprecipitates; recovering the said solid silver salt of 5- cyanotetrazolethus-formed; adding water thereto to prepare an aqueous menstruum of thesame; passing hydrogen sulfide gas through said aqueous menstruum;concurrently forming silver sulfide precipitate; removing the latterprecipitate; and, thereafter, evaporating the residual filtratecontaining S-cyanotetrazole to thereby recover the latter.

3. A process according to claim 2 in which the alkali metal nitrite issodium nitrite.

4. A process according to claim 2 in which the cyclization step iscarried out at a temperature of about 5 C.

References Cited in the file of this patent

1. A PROCESS FOR THE PREPARATION OF 5-CYANOTETRAZOLE WHICH COMPRISES THESTEPS OF: REACTING 1-CYANOFORMIMIDIC ACID HYDRAZIDE WITH AN ALKALI METALNITRITE IN THE PRESENCE OF NITRIC ACID AND A SOLUBLE SILVER SALT TOEFFECT NITROSATION AND CYCLIZATION OF SAID HYDRAZIDE; AND THEREAFTERRECOVERING 5-CYANOTETRAZOLE THUS-FORMED.